To provide a small-sized light-weight power-generating apparatus which can generate a predetermined power, irrespective of the operating state of a connected prime mover.

The power generating apparatus comprises a generator having a rotor, having a plurality of phase windings and a stator, an exciting means for supplying an AC voltage to the windings of the rotor; a current-detecting means for detecting the field current of the rotor; a phase arithmetic means for calculating the phase of the AC voltage to be supplied by the field means; a first conversion means for converting the field current into a plurality of phases, to generate d-axis and q-axis field currents; a current command arithmetic means for calculating the current command to the d-axis and q-axis field currents; a current control means for calculating the d-axis/q-axis field voltage commands in the d-axis and q-axis directions; and a second conversion means for d-q-axis converting the d-axis/q-axis field voltage command to generate a voltage command for controlling the AC voltage to be supplied from the field means C.